Ööpäeva

Ööpäeva is the genitive singular form of the Estonian noun ööpäev, a term that refers to a 24‑hour period or to the span of a day and night. In everyday language, ööpäev can denote either a calendar day or the full 24‑hour cycle, depending on context, while ööpäeva serves as the possessive form used after prepositions or to express “of the day.”

Etymology and meaning: The word combines the elements öö (night) and päev (day), reflecting the full cycle of day and night within one 24‑hour period. This etymology underscores its primary sense as a complete daily interval rather than a single moment.

Usage and examples: The term appears in scientific, legal, and meteorological contexts, as well as in general descriptions of time. Examples include: Ööpäeva pikkus on umbes 24 tundi. (The length of a day is about 24 hours.) Temperatuur võib ööpäeva jooksul muutuda. (The temperature can change during a 24‑hour period.) The phrase ööpäeva jooksul is used to mean “during a 24-hour period.”

Relation to related terms: Ööpäev is closely related to päev, meaning day, and to öö, meaning night. While päev focuses on the daylight portion or a calendar day in common usage, ööpäev emphasizes the entire 24‑hour cycle that includes both day and night.

See also: päev, öö, ööpäev, timekeeping terminology.